Sewage Pump question.

I installed a basement bathroom, and had to install a sewage pump & basin (Flotec). I'm having a problem with the sewage pipe banging, when the pump stops; I think it's because the manufacturer said the Check Valve had to be installed horizontally to avoid solids from preventing the valve from opening. This means I had to install the PVC so that it comes vertically out of the basin, turns 90 degrees, connects to the check valve, turns 90 degrees to vertical, then across the ceiling to my main stack. I believe the bang is caused by the horizontal span not being secured, but I don't see any way to secure it without building a support platform, and strapping it to it (There aren't any walls or studs near it). I think it would've been better to put in a vertically mounted check valve, but I don't know of any that would work reliably. Any ideas would be greatly appreciated.

The bang is caused by the 8 feet of water in the vertical pipe, whether it is 2' above the valve and 6' below it, or 6'above the valve and 2' below it. The entire column of water acts on the valve regardless of its actual location. You may need a different check valve, but they will all "bang" when they close. Some are just quieter than others. And the valve can be vertical regardless of what Flowtec says. If there is going to be solids in the pipe they will accumulate against the horizontal valve just as readily as a vertical one.